Distilling process and apparatus



July .19, 1932- E. H. LESLIE E'r AL 1,868,465

DISTILLING- PROCESS AND APPARATUS Filed June'29. 1925 3 Sheets-Shee lJuly 19, 1932- E. H. LESLI ET AL 1,868,466

DISTILLING PROCESS AND APPARATUS Jl Jg.

FEOM PUMP 62 I JOL* ,eas/0MM( met July 19, 1932.

El H. LESLIE ET AL DISTILLING PROCESS AND APPARATUS l Filed June 29,1925 3 Sheets-Sheet 3 CONDE/V651? Misma July 1e, 1932 Arnia oFFieE.

EUGENE E. LESLIE AND EDWIN' M. BAKER, 0F ANN ARBOR, MICHIGAN DISTILLINGPROCESS AND APPARATUS Application filed June 29,

acter above mentioned. A further object 0fv the invention is to provideapparatus whereby the foregoing object may be achieved while at the sametime utilizing to a -large extent previously installed refineryequipment, such as batteries of stills, by associating with' suchequipment suitable fractiona-ting apparatus,

thus providing a complete apparatus system appropriate for practicingthe invention at 'the lowest cost lconsistent with the accomplishment ofthe desired result.

While the invention is not restricted to the field of petroleumdistillation, its greatest pres-ent utility is in that field.Accordingly in -explaining; the. underlying principles of the inventionhereinafter, reference will be made more particularly to petroleumdistillation by way of a concrete illustrative eX- ample.

In the continuous distillation of petroleum 3D as heretofore practiced,the operating equipmentis usually composed of a continuous stillbattery, thestills of which may or may not be fitted with'towers,dephlegmators, or in general, fractionating condensers. Assum- 40 ingthe use of some form of fractionating condensers with the stills, theconventional mode'of operation has been as follows:

The incoming loil is first passed through heat exchangers and thenflowed through the 45, stills in series which are suitably heated toeffect continuous stage-wise distillation of the oil passing seriallythrough the stills of the battery.l The distillation vapors, which aresuccessively heavier from the first to the lastl still of the battery,pass from each still '3.925. Serial No. 40,421.

into its associated fractionating condenser wherein a relatively heavyportion of the vapor condenses, the condensate flowing back to thestill. Vapors from the tops of the fractionating condensers pass towater-cooled condensers, and the resultant condensates are cooledseparately. The distillate from the first still lof the battery(assuming crude petroleum to be the oil to be distilled) is found upontest to be almost wholly within the a0 gasoline boiling range Aas fixedby standard Navy specifications, for example. For instance, if the crudeoil contains 30 per cent of gasoline, the distillate from the Yfirststill comprises commonly from 5 to 15 per cent 65. of the crude oil,depending upon the particular mode of operating the still battery. Thedistillate from the second still tests perhaps 90 per cent of gasolineboiling range, the other 10 per cent probably boiling somewhat 70 above45370 F. However, this high boiling portion can be mixed into thegasoline when the light distillate from the first still is mixed withthe distillate from the second still. The distillate from the secondstill may be 76 say 10 to l5 per cent of the total volume of crudeflowing to the battery.

Usually only about orge-half to threefourths of the distillate from thethird still will be found to be of gasoline boiling ran-ge, 80 and thisconstitutes what is known as benzine in refinery parlance. Thedistillate from this third still may in some cases be as much as l5 to2O per cent of the crude oil,

especially where the distillates from the first and second stills wereminimum percentages. In order to secure the gasoline content of'thisdistillate from the third still, it is customary to re-run the' benzinein so-called re-run stills, which stills are fireeand-steam stills,usuallyfitted with some form of dephlegmator to permit. more effectiveseparation. The distillate from these re-run stills is of gasolineboiling range band is mixed into the gasoline product. The bottoms orunvaporlzed portion is a light kerosene.

Assuming the battery to consist of four stills, the distillate from thefourth or last still comprises the gas oil, and in some plants includesalso what is the heavy end of the 10 kerosene. 'Where heavykerosenes areto be made, this fourth distillate may be re-run to recover such heavykerosene. More usuum The prior practice above outlined is open tonumerous ser1ous objections from the standpoint of the practicalrefiner. In the lirst pla/ce, it is impossible by this procedure toobtain from a given crude oil the maximum amount of distillate that willpass the standard specications for gasoline boiling range. Furthermore,the necessity of employing rerun stills greatly increases thev firstcost of the installation and its subsequent upkeep, not to mention thelarge ground space occupied by said re-run stills. The system as aiwhole is also thermally ineiiicient and uneconomical in operation. Theseand other objections are overcome by the process of the presentinvention and certain additional advantagesl are alsoattained, as willappear more fully from the description hereinafter'.

In contrast to prior methods of continuy ously distilling petroleum inaccordance with the general 'procedure above outlined, 'the process ofthe present invention involves sharp fractionation of the. distillationvapor coming from each ofthe stills of a battery, in.

such manner that everything that can be in.- cluded in the gasolinelunder standard speciflc'ations leaves the distilling system and is'obtained in the `gasoline condensate, while everything that should notbe included as gasoline leaves the'system either in the form ofresiduum, or of gas-oil, kerosene, or the like, which may be withdrawnat one or more intermediate points inthe system. Stated generally, thisresult is achieved by conductmg the distillation vapors from all of thedistilling units of the battery into a rectifying system character inthe sense rthat the liquid' therein with which the distillation ,vaporscountercurrently contact is provided solely by reiiuxin into therectifying system condensate V from t e rectidvapors that leave saidsystem. Ordinarily said rectifying system takes the form of a singlecolumn fractionator, using the term fractionator in the correct 55.technical sense by which it is sharply disltinguishied from apparatus ofthe fractionating condenser type. While a structurally unitary or singlerectifying column or fractionator is generally the most convenient formof unitary rectifying system to employ in the practice-of the presentinvention, this is not a rigid requirement within the broad scope of theinventive idea here involved so long as the conditions of operation hereemphasized are observed, namely, that the only which is essentiallyunitary in` counter-flowing liquid introduced as such into the aforesaidrectifying system shall be refluxed condensate from rectified vapors`leaving the system.

(Certain very importalltpractical advantages result from the novelprocedure characterizing the invention. In the iirst place, thenecessity for re-run stills is entirely eliminated, while in place ofsuch equipment itis only necessary to install a rectifying column ofwhich the cost is relatively very small as compared to that of abatteryof re-run stills and which occupies only a fraction ofthe groundspace required by such a battery. Furthermore, as will be more `fullyhereinafterpointed out, the yield of salable gasoline is substantiallyincreased and a material economyof heat units is effected, not tomention other advantages that will appear as the description proceeds.85`

The underlying principles of the invenf tion can be further explained tobest advanl tage in connection with a detailed description of a typicalpractical embodiment thereof that has been found to give good results inpractice. 1n this descriptiom reference will be made to the accompanyingdrawings which illustrate more or less diagrannnatically typicalapparatus installations useful in carrying out the process. 'Referringto these drawmgsa i l Fig. 1 is a diagrammatic view in elevation of atypical plant embodying the yprinciples of the invention, wherein asingle rectifying column or fractionator is associated with a battery offour stills of the ordinary pot type;

Fig. 2 is a similar view of a plant in which a battery of pipe stillsisused in place of the pot stills of Fig'. 1;

Fig. 2a is a cross sectional view of one of the pipe stills; and- Fig. 3is a similar view of another plant also embodying the broad principlesof the invention in which, however, the rectifying systemdiffers-structurally from that illustrated in Figs. 1 and 2.

Referring -iirst more particularly to Fig.

1 of the drawings, thevcru'de petroleum .or other oil to be distilled ispumped by the pump 10 through heat exchangers 11, 11", 11, 11d, in whichexchangers the heat from the hot residuum leaving the system is transnferred in part to be incomingcrude. From. v the last heat exchanger, theo1l iows b pipe 120 12 to the first of a series or battery o stills'Nos. 1, 11,111, 1V. From still No. 1, the

oil passes by pipe 13 into still No. I1, thence by pipe 14 into stillNo. 111, thence by pipe 15 into still No; 1V. From still No. 1V, the 125'hot outiowing residuum exits through pipe 16 and is forced by pump 17through the heat exchangers before mentioned, countercurrently to theincoming crude\petroleum as already described.

soA

Stills Nos. I, II, III, IV are of any suitable type or form and are setin any conventional or suitable way. In the present instance, saidstills are horizontal, cylindrical stills of the pot type, supported inbrick work in the usual manner with their upper exposed portions coveredby heavy insulating lagging. The stills and the interconnecting pipingare so arranged that the oil iows into one end of still No. I and out ofthe opposite end into .still No. II, then out of the opposite end ofstill No. II to still No. III and so on. The interconnecting pipingbetween the stills should be of suilicient size to permit easy flow of.oil from one still to the next without undue back pressure. When normalrunning conditions have been established, the oil in the respectivestills of the battery stands at successively lower levels, as indicatedat L1, L2', L3, L4, due to corresponding differences in back pressurefrom the rectifying system to be described presently. Of course, if thestills themselves are set at successively lower levels, the depth of oilin each still may be the same'. In any case, the oil level in any givenstill should always be such'that the heating surface of the still iscompletely covered with oil in order that local overheating may notoccur at points where the still bottom is exposed to the direct firebeneath the still.

'Ihe' vapors from each still are introduced into a suitable rectifyingor fractionating -system at suitable points. In the installationillustrated in Fig..1, this rectifying or fractionating system consistsof a single fractionating column, indicated generally at C,.

having an appropriate number of bubblercap sections which may be of anyusual or suitable design. It is not essential that the rectifying columnbe of the bubbler-cap type, the essential point being that the apparatusbe of such character `as to afford full opportunity for countercurrentlycontacting upwardly flowing vapors with downwardly flowing liquid underconditions ensuring an approximation to equilibrium conditions at allpoints in the rectifying system. Such conditions can be realized incertain other forms of columns, such as packed columns, for example. Ingeneral, the distillation vapors from the several stills of the batteryshould be introduced into the fractionating column at such respectivepoints that the vapors introduced at any one of said points will be, asnearly as is practically possible, in equilibrium with the vapor andliquid within the column at that point when the entire battery" ofstills land the column are functioning smoothly and properly in theregular course of operation.

In the present instance, it will be seen that the vapor from still No. Iis almost all gasoline, although of necessity it contains a smallproportion (the equilibrium proportion) of the higher boiling componentsof the petroleum from which the vapor was evolved. Consequently, thisvapor is introduced into the column near the top but such a sufficientnumber of sections below the top that the small proportion of heavy oilmolecules contained in this vapor will be removed by the process ofcountercurrent contacting within the fractionating column.

The vapor from still No. IV is the least rich in volatile constituentsand is therefore introduced into the bottom section of the fractionatingcolumn C. The vapors from stills Nos. II and III are introduced atappropriate points in the column intermediate the points at which thevapors from stills Nos. I and 1V are introduced. As before stated, thegeneral principle governing the selection of the point for introducingthe vapors from any of the stills into the column is that the pointselected should be such that the introduced vapors will be substantiallyin equilibrium with the vapor and liquid within the column at that pointwhen the entire battery of stills and the column are functioningsmoothly and properly in the regular course of operation. In any givencase it will be necessary to take several factors into account and tofollow the general rule that the vapors should enter the column at thepoint where they will be most nearly in equilibrium when the column isfunctioning properly.

In the present example the fractionating column consists of'sixteenbubbler-cap sections, but the number of sections may of course be varieddepending upon the various factors of operation'to be taken intoaccount. Each section is provided with a drawoff pipe 18 for liquid,which draw-off pipe is provided with a valve and trap, as indicated.These draw-off pipes enter a header 18a. Vapor from the top of thecolumn is led by vapor pipe 19 to condenser 2O which may be of anydesired form. In the present instance the condenser consists of a worm.2l arranged within a tanlrlled with coolfrom the fractionating column.As will be pointed out hereinafter, however, it is sometimes anadvantage to operate this condenser in such ma er that` the lighterportions of the gasoline vapors escape condensation therein, and whenthis procedure is followed, such lighter vapors pass on into a secondcondenser 22,-yielding a light condensate which is collected in cooler23, so-called fixed gases or normally uncondensable vapors being ventedfrom the system at 24. The condensate produced in condenser Q0 passesfrom the condenser into a dividing box 25. It will be seen that theliquid enters the box at one end andthence flows through two weirsS26-27, the horizontal opening of these weirs being adjustable by manualcontrols S28-29, as indicated, so that the proportion of the distillateflowing through the respective Weirs may be adjusted to any desiredproportion. The discharge through Weir 27 passes vthrough a cooler 30and thence to any suitable receiving tank or other place of storage (notshown). .The discharge through 4the other Weir (26) is directed back tothe top of the fractionating column and constitutes the reux to thecolumn. This flow.

may be by gravity or, as in the case here illustrated, the discharge ofWeir 26 goes to a receiving tank 31 and is pumped therefrom by pump 32/into the top section of the column, as indicated. In the installationhere shown, the feed of liquid from receiving tank 31 into the top ofthe fractionating column is autpmatically controlled by the level oftheli uid in the receiving tank by oat-contro led means indicateddiagrammatically at 33 and arranged to govern the actuating mechanism ofthe pump 32, the arrangement being such thatthe pump automaticallydelivers reux to the top of the fractionatin'g column at the same ratethat the redux liquid runs into the receiving tank to which the suctionside of the pump is connected.

The liquid condensates received in coolers 23 and 30, respectively, areusually mixed 'together and constitute the gasoline product of theplant.

, It will be seen that in the specific procedure just described, thereflux liquid returned to the top .of the fractionating column is notrich in very light gasoline vapors, these latter largely escapingcondensation in condenser 20 and therefore not yielding any liquidproduct entering dividing box 25 from which reflux is supplied to thecolumn. In some cases it is advantageous thus to avoid returning verylight gasoline fractions to the. top of the column,.and while theprocess of the invention does not necessarily involve this specificprocedure, it forms a desirable feature of the invention in its morespecific aspects and has been found to Work Well in practice.

At 34 is indicated a small exhausting column linto which liquid. from`the bottom of the main fractionatingcolumn C may be run.

The use of this'exhausting column is optional and is dependent upon thenature of the product that it is desired to obtain from the bottom ofthe column. Ordinarily, the apparatus may be sorun that the liquid fromthe bottom of the column contains a negligible. proportion of gasoline,say less than one to three percent. If'it were desired to produce fromthe bottom of the column a liquid product containing no gasoline andpossibly not even a lighter part of what is normally kerosene, thiscould be done by using the exhausting column referred to. Heat' must besup-- plied in the form of vapor to the bottom of the exhausting columnand this is done by means of a Ismall auxiliary heater.v (not Lesaaegoshown). In the present example the liquid from the bottom of the mainfractionating columnC -is shown entering the top section of theexhausting column 34, while the vapors lfrom the exhaustingl columnleave through of the liquid leaving the bottom of the column C` liquidleavesthe' bottom of said column C'through pipe 36 which delivers it tocoolerf37. In the present example this liquid may be assumed to be agas-oil'fraction. If the kerosene can not' be included either in thegasoline or inthe gas-oil fraction, it must be Withdrawn at someintermediate point along the column. In the present instance, thekerosene fraction is Withdrawn through pipe 38 and header 18a from -thatsection of the column C indicated at 39. This kerosene fraction isdelivered into an exhausting column 40 which contains a heating coil 4lin its base. The vapors leave the column 40 through pipe 42 and passinto condenser 43 Where condensate is formed and reiluxes through pipe44 back to the top of the exhausting column 40;.

while the uncondensed vapors are delivered through pipe 45-tovapor-manifold 46 from which they can be directed into any desiredsection 'of the fractionating column C. In this way', liquids of variouscompositions can be removed from the column C through suitably locateddraw-off lines 38, 38a, 38h, 38,

and any one of the liquids so removed may be treated in an exhaustingcolumn as desired. That is, if it be found that from no section of thecolumn can a liquid of exactly the desired composition be Withdrawndirectly, this procedure can be adapted to obtain a liquid of .thecomposition desired. A liquid can be withdrawn from some one Section ofthe column C that. is of 'such composition that its` higher boilingportion. is satisfactory.

. The volatile end of 'this liquid can then be removed in an exhaustingcolumn and the vapor so formed returned to the column C at the pointWhere it is most nearly in equilibrium when the column is operatingnormally.

If desired, that portion of the auxiliary exhausting column 40 above thefeed section into which liquid is delivered through pipe 38 may beomitted; The sections above this feed section perform a rectifyingfunction, and inl somel instances would be unnecessary because it .wouldbe immaterial Whether a portion of the heavier components in the liquidfed in throu h pipe 38 was onnot vaporized and returne to the maincolumn C. If 130 34. -'Under such circumstances it would in mostinstances be desired` to remove perhaps not more than ten per cent byvolume of the liquid fed to the top of column 40. Consequently thereflux ratio would be 8 or 9 to 1, which Would be ample for allrequirements. v

Reference has been made hereinabove to removal of intermediate productsas liquids. They may, however, be removed as vapors; and to this end therectifying or fractionating system may be provided with oftake meanswhereby vapor may be lWithdrawn from' any desired section or locality.In order to avoid `complicating the drawings, such means are notillustrated here but are of sufciently Well understood character not torequire special explanation. The choice as to whether a given desiredproduct should be removed as a liquid or as a vapor depends upon Whetherit is desired to have such product free from volatile components or freefrom heavy components and of particularly good color. In the first case,it should be removed as a liquid; in the second, as a vapor.

Itis also feasible and desirableunder some conditions to employ anauxiliary column into which vapor is introduced from the main column,but to which auxiliary column no heat is supplied in additionto thatcontained in the vapor itself. In such an arrangement, the auxiliarycolumn should be provided with a reflux condenser and a certain amountof liquid should be reluxed to the top of said column, a-vapor productleaving the upper part of the column and being condensed and collected.The liquid from the base of 'this auxiliary column, which liquid maydesirably be thermally equivalent to the liquid refluxed to the top ofsaid column, may either be returned into the main column at anappropriate point Vor may be collected separately as a product.

In starting the battery intoloperation, it may be found desirable insome Acases to return the liquid from the bottom of the column C tostillvNo. III for a time. This is because normal yand regular operationof thesystem Will not be attained immediately upon starting up, andconsequently gasolinein morethan the normal small amount Will be foundfor a time in the liquid exiting from the bottom of column C. A valvedreturn line 47, branching from line 36 and entering line 14, istherefore provided for permitting temporary return of liquid from thebottom of column G to still No. III., It is preferable to return thisliquid to still' No. III rather than to still No. IV becausere-vaporization and recovery of all of the gasoline content of thereturned liquid is thereby rendered more certain.

It is to lbe especially noted that the distillation vapor from eachstill of the battery is sharply fractionated in operating in accordancewith the process of the invention. This is true even of the vapor fromstill No. I. The vapor from this still contains only a small amount ofhigh-boiling hydrocarbons;

and although it vWould be possible to include these hydrocarbons in thegasoline Without making a product having an end-point above 437 F., itis undesirable to do this because,

just to the extent that these higher boiling hydrocarbons are includedin the gasoline, the'average boiling point of the gasoline is raised,particularlyl in the later stages of the distillation test to which thegasoline is subjected understandard specifications. According to thepresent process, the greater part of the undesirably heavy hydrocarbonsthat formerly could bekept out of the gasoline fraction only by specialmeans such as redistillation, can be easily excluded; While much of thegasoline formerly going into the gasoil fraction is recovered.

In one Way of operating the illustrated still battery in practicing thepresent process, the vapor from still No. II may correspond very closelyto the benzine fraction above referred to as obtained in prior practice.In the present process, these benzine vapors are introduced into thecolumn, as shown, several sections below the point at which the vaporsfrom still No. I are introduced; and by .the action .of the column, thisbenzine vapor is fractionated in such manner that only the gasolineportion exits from the column as a vapor, While the noni-gasolineportion passes down the column 'as a liquid. The vapor from still No.III, although it contains no light gasoline, contains a moderateproportion of hydrocarbons that boil below 437 F. This is also-true ofthe vapor from still N0.. IV, although to a less degree. Both of thesevapors are introduced into the fractionating column at the respectivelylower points indicated and are similarly fractionated so that only suchportion thereof as can properly be included in the gasoline exits fromthe top of the fractionating column. As a result of proceeding in themanner above described, re-running is completely eliminated; and in aplant Where re-run stills lform a part of the original equipment, there-run stills may vvtherefore be entirely dispensed with or used forsome other purpose. A further advantage of the novel process, alreadymentioned above, is the increased yield of marketable gasoline. InAactual practice it has been found that employment of the novel processin distilling a given crude, for` example, results in an increased yieldof gaso line amounting to from 15g to 30 per cent of the yield obtainedfrom the same crude disuned by the' described method df the prior mflfuel consumption can be cut as much as per cent or more by distillationin accordance with the present invention as above described.

In addition to the advantages already mentioned, there are otherspossessed by the invention vthat are of material importance.

For example, the color of the gasoline product obtained is improved overthat obtained 'in prior practice, and consequently less acidis' requiredin refining. Again, the easier control and more fiexible operation ofthe battery `as a whole is marked, and consequently the operating costsfor labor and supervision are reduced. All these advantages attainableby the present invention result in increased rev-l enues and reducedexpenses amounting to many thousands of dollars monthly in a plant ofsubstantial size running several thousand barrels of oil daily as suchplants quite commonly do.

The plant illustrated in Figs. 2 and 2a. is generally similar in mode ofoperation to that illustrated in Fig. 1 and may be used with equal andin some cases greater advantage in practicing the novel process. Theprincipal difference is in the employment of pipe stills as primaryvaporizers instead of4 horizontal cylindrical stills. In the presentinstance the prlmary vaporizing portion of the system conf sists of abattery of pipe stills which may,-for example, comprise five pipe coilunits, 50,

51, 52, 53 and 54, serially related and all housed within a suitablefurnace structure indicated generallyat 55, the interior of the furnacestructure being divided vertically into four sections, by partitionwalls 56 and horizontally by apertured partition walls 57. Each sectiondefined by the vertical furnace walls has a combustion chamber 58 at thetop, from which flame and hot combustion gases pass downwardly aroundone of the pipe coils 51, 52, 53, 54, and thence through apertures 59 inthe wall '57 and around pipe coil 50, the gases finally passing to asuitable stack -through `due 60.

The crude oil enters the system through a system of heat exchangersindicated generally at 6l and similar to that described in connectionwith Fig. 1; passes thence through line 62 into pipe coil 50 which islocated in the lower part of the pipe still battery and fwhich thereforeis subjected to the heating effect of combustion gases at asubstantially lower temperature than are pipe coils 51, 52, 53 and 54.From heating coil 50, the oil is delivered through linev 63 into a 4Hashvaporaccadde sist of upper and .lower sections 65, 66, filled 7n withsuitable packing, such as ring packing or the like, 'between whichsections is located a distributing baffle 67 upon which the superheatedoil from pipe coil 50 is delivered through line 63. ln this vaporizerthe hot oil -75 is rapidly distributed over an enormously extendedsurface and a vapor flashed oif which approximates the equilibrium vaporof the liquid for the temperature and pressure prevailing in thevaporizer. The vapor,

thus flashed 0H, preferably scrubbed of its entrained liquid and to someextent recti'- fied in passing through the upper packed section 65,leaves the vaporizer through line 68 and is delivered thereby into theupper part of fractionating column C( which may be similar in allrespects to the fractionating column C of Fig. 1. `The liquid remainingunvaporized in vaporizer 64 is withdrawn therefrom by pump 69 whichforces it through pipe 70 into and through pipe coil 51 in the pipestill furnace where said oil is superheated at a substantially highertemperature than the oil in pipe coil 50. From i pipe coil 51 thesuperheated oil is delivered fthrough pipe 71 into a second'flashvaporizer l 72 which may be essentially similar to Vaporizer 64 alreadydescribed. Vapors flashed ofi in vaporizer 72 are delivered through line73 into a somewhat lower section of the fracf tionating column C', asshown; while separated liquid oil is drawn from vaporizer 72 throughtrapped line 74 by a suitable pump (not shown) and forced through thenext pipe coil .in series, namely, pipe coilv 52. In adnanner similar tothat already described in connection with :pipe coil 51, the oil passingthrough pipe coil 52 is superheated at a still higher temperature and isdischarged into a third vaporizer (not shown), the vapors flashed offtherein being introduced into a still lower section of the fractionatingcolumn C through vapor line 75, while the separated liquid oil passesinto and through pipe coil 53 in the furnace where it isstill furthersuperheated and then delivered linto a. fourth vaporizer (not shown).From this fourth vaporizer, the flashed-off vapors pass into thefractionating column through vapory line 76, while the separatedliquidoil passes into the last pipe coil 54 ofthe battery where it isIsuperheated to the maximum temperature employed and then delivered to afifth vaporizer (not shown) from which the separated vapors pass intothe base of the fraccylindrical type. Furthermore, by employ-l ingvaporizers of the type illustrated at 64 and 72 in, conjunction withsuch pipe stills, a much cleaner separation of substantially equilibriumvapors from the superheated oil is initially obtained prior to theintroduction of vapors into the fractionating column from the severalstill units than is possible when a system of the type illustrated inFig. 1 is employed.l This renders satisfactory win- -ningpf the gasolinecontent ofthe oil more certain, but in broad principle the system shownin Figs. 2 and 2a does not fundamentally differ from that shown inFig. 1. y j In the system illustrated in Fig. 3, a battery of fourhorizontal cylindrical stills is employed as in the case of the systemillustrated in Fig. 1. The rectifying system, however, differs from thespecific form thereof illustrated in Figs. 1 and 2 principally in that,instead of a single rectifying or fractionating column, there areemployed a plurality of rectifying or fractionating units,l

one for each of the stills of the battery, which are so relatedstructurally and functionally, however, as nevertheless to constitute aunitary rectifying system within the meaning of this expression ashereinabove defined. Thus, the vapors from stills Nos. I, II, III and IVpass into the base of rectifying units 80, 81, 82 and 83, respectively.Liquidfor countercurrent contacting with the vapors in the rectifyingunits passes in series through the four units in the order 80*81-82-83.

-tifying system as such is the gasoline product refiuxed from thedividing` box 25 into the top section of rectifying unit 80. The' liquidleaving the bottom of each of the rectifying units 80, 8l and 82 is leddirectly into the top of the next succeeding unit ofthe series, asshown; the liquid leaving the bottom -of rectifying unit 83 being, in atypical instance, a gas-oil substantially free of gasoline constituents.On the other hand. the vapors leaving the top of rectifying unit 83 areintroduced into the bottom of the next preceding unit 32 in the series,and so on, the completely rectified gasoline vapors finally 'leaving thetop of rectifying unit 80 and entering the condenser as shown to yield agasoline condensate of which at least a portion is refiuxed to the topof said unit as already stated. 65 The system just described may includealso The only liquid oil introduced into the recauxiliary exhaustingcolumns of the type described in connection with the systems shown inFigs. 1 and 2, where it is desired to draw intermediate liquid productsfrom different portions of the rectifying system in order to obtainproducts of certain specified characteristics.

It is also feasible to so arrange the piping connections that any one ofthe four'rectifying unit-s, with itscooperating still, may be cut out ofthe system for repairs or cleaning out, Without interfering withoperation of the remaining units and stills in the manner described.Such flexibility is at times very desirable in a system of this kind.

The general mode of operation of such a system as this does not differmaterially from that of the other novel systems hereinabove described;but in some situations itisconvenient to split up the rectifying systemstructurally into a plurality of serially related units of the characterdescribed, and by arranging the apparatus as described, it is possibleto do this while observing the essential conditions of operationcharacterizing the invention and realizing its benefits wholly or inlarge measure.

In referring to conditions of operation such that introduction ofcounterflow liquid into the system is to be avoided at points other thanthat adjacent where rectified vapors leave the system, it is notintended to exclude from .the scope of the invention herein dis closedand lclaimed the case where it may be necessary or advisable, as atemporary measure or otherwise, to re-run a distillate (e. g. so-calledbenzine) for separation into gasoline and a heavier fraction byintroducing such distillate into some appropriate point 1n the maincolumn.

1What we claim is:

1. Distilling apparatus comprising 1n combination, a plurality ofstills, connected in series for flow of liquid through the entireseries, a single rectifying or fraotionating column, vapor linesarranged to conductvapors from the several stills separately intodifferent sections of said column adjacent the top and bottom of thecolumn and at intermediate points thereof where the vapors arerespectively substantially in equilibrium with the vapor and liquid ofthe column, condensing means into which vapors pass from said column,means for refluxying condensate to the upper part of the colcombination,a plurality'of stillsl connected in-series for flow of liquid throu hthe entire series, a single rectifying or ractionating column, vaporlines arranged to conduct vapors from the several stills separately into.diiierent sections of-said'column at points thereof where they arerespectively substantially in equilibrium with the vapors and liquids ofthe column, condensing means into @which vapors pass from said column,means for 'reliuxing condensate to the Aupper part of said column, anauxiliary exhausting column, means for diverting liquid thereinto from asection of said fractionating column, and means for returning to saidfractionating column vapor from said exhausting col-l lIIIlIl.

3. The process of distilling liquids of mixed composition whichcomprises passing l such a liquid serially through a plurality ofsuitably heated distilling chambers, conducting evolved vapors from allof said distilling chambers into a unitary rectifying system, condensingrectified vapors leaving said rectifying system, providing a rectifyingcounterllow "of liquid in contact with said vapors in said rectifyingsystem by refluxing at least a part of the condensate'from saidrectified vapors to said rectifying s stem at a point adjacent wheresaid recti ed vapors leave Asaid system while avoiding introduction ofcounterilow liquid, as such, elsewhere into said system, the evolvedvapors from 'each of said distilling chambers being introduced into thatpart of said rectifying system where they will be respectivelysubstantially in equilibrium with the vapor and liquid in said system,removing from said rectifying system an intermediate fraction 40 of anapproximately desired composition, ex-

hausting said fraction of-its more volatile portion to obtain a productof an exactly predetermined composition, returning said more volatileportion to the 'rectifying system at such point as to be in substantialequilibrium with the liquid and vapor in said system, and withdrawing. adesired distillation roduct from a point in the combined recti ying andcondensing system. In testimony whereof we hereunto aliix oursignatures,

EUGENE H. LESLIE. EDWIN M. BAKER.

